在进行定制化开发中，对于限制app卸载的功能也是常有的功能，就是常说的app卸载黑名单功能，而
app的安装和卸载都是有pms进行管理的
接下来看下PMS的源码

/**
 *  This method is an internal method that could be get invoked either
 *  to delete an installed package or to clean up a failed installation.
 *  After deleting an installed package, a broadcast is sent to notify any
 *  listeners that the package has been removed. For cleaning up a failed
 *  installation, the broadcast is not necessary since the package's
 *  installation wouldn't have sent the initial broadcast either
 *  The key steps in deleting a package are
 *  deleting the package information in internal structures like mPackages,
 *  deleting the packages base directories through installd
 *  updating mSettings to reflect current status
 *  persisting settings for late